It is well known that the change of direction of an electromagnetic wave caused by a local change of its propagation velocity is denoted a light refraction which is described by an index of refraction n. The refraction occurs “towards the perpendicular” when a beam of light enters a medium comprising a greater index of refraction (for example from air into water or glass). When light waves or other electro-magnetic waves impinge from one medium (for example air) onto another (for example glass) whose index of refraction differs from that of the former a part of the light is reflected, another part is subjected to a deflection according to the law of refraction by Snellius. Upon a transfer into a medium comprising a greater index of refraction the beam of light is refracted towards a perpendicular line of the separation plane, therefore becomes steeper, and in a medium comprising a smaller index of refraction is refracted away from the perpendicular line. In the latter case there will be a total reflection when the angle of incidence c exceeds a certain value. For example, air has an index of refraction of about 1.00029 and transparent plastics and glasses have indices of refraction between about 1.3 and 1.7. Based on this physical effect is the mode of operation of fiber-optic light guides which have become widely used as glass fibers for data communication.
Known in vehicle lamps is the use of fiber-optic light guides as substantially rod shaped elements by which the light of a light source, which often has one or more compact light sources, is directed to a for example poorly reachable location inside of the vehicle lamp and is decoupled there and thereby is made visible. The light such guided is not noticeable from a viewing direction directed lateral perpendicular to the light guide because the beams of light impinge relatively flat at the refraction media transfer plane in the fiber-optic light guide and are reflected completely. At designated light emission locations light decoupling means are provided for, which are formed as optical prism, lenses or a surface roughness.
For example, DE 102 08 140 A1 shows an illumination equipment for motor vehicles comprising a main light source contained in a housing and an auxiliary light source. It is provided for that the radiating surface of the light emitted by the main light source is at least partially interspersed with at least one light guiding element, wherein the light of the auxiliary light source is coupled into the light guiding element.
For example, known from DE 103 28 216 A1 is an illumination equipment for vehicles, in particular a signal lamp, comprising a lamp and at least one rod-shaped light guide comprising a light coupling plane arranged in the radiation area of the lamp. In doing so, the light guide in its outer perimeter has several optical decoupling elements shifted with respect to each other at which inside of the light guide light impinging thereon is reflected such that it leaves therefrom at a perimeter area opposite of the respective decoupling element of the light guide. Between the decoupling elements decoupling-free intermediate areas are provided for. In doing so, the length of the intermediate areas and the length of the decoupling areas may be varied along the length of the light guide. In this manner it is to be achieved that along the extension direction of the light guide a brightness distribution of the light decoupled from the light guide, which is deviating from the respective amount of light available in the light guide, is rendered possible. Nevertheless, the light guide shall have a uniform appearance. In doing so, the light guide generally is based on the principle of total reflection inside of the light guide, until the light impinges a decoupling element and then is redirected such that it impinges the wall of the light guide in such an angle that it may be decoupled therefrom. When the light does not impinge onto a decoupling element the light may not leave the light guide and is transmitted to the end of the light guide. Then, the light is reflected back at the end of the light guide and impinges onto a further diverting side of the decoupling element and thereby is decoupled from the light guide in a common manner.
DE 10 2006 011 108 A1 discloses the use of fiber-optic light guides for illuminating the inner edge of a vehicle door or a trunk lid or the like, wherein the light guide follows the contour of the edge of the door.
DE 10 2005 042 675 A1 discloses a vehicle in which the light of a central light source is guided via extended light guides to several illuminants located in front and rear areas of the vehicle.
DE 10 2005 019 093 B4 discloses a multiple light guide used in a vehicle lamp which constitutes a merger of several light guides extending with an angle to each other. The beams of light from each of the light guides cross each other and each leave the light guide at an individual light decoupling position.
DE 10 2006 027 970 A1 discloses a headlight in which the head lamp unit is encased by a transparent hollow part which serves as the light guide and is dedicated to the operation of the daytime running light. This solution implicates additional costs and widely determines the embodiment of a headlight.
DE 103 28 216 A1 discloses a vehicle lamp comprising a rod-shaped light guide which is used to direct the light of a point light source inside the housing of a lamp into a desired area which otherwise may only illuminated poorly. DE 10 2005 059 958 A1 also discloses an illumination equipment which uses an additional substantially rod-shaped light guide in which the light decoupling elements are formed as inclined faces. DE 10 2005 038 154 A1 discloses a vehicle lamp comprising a rod-shaped light guide which is irradiated by several light sources in order to provide for a more uniform illumination of a lengthwise extending light decoupling area. Such light guides are additional components which render a vehicle lamp more costly and more complex. In addition, at the surfaces of additional light guides dust and deposits may be deposited also inside of a lamp housing and may interfere with the operation as well as the optical appearance.